Postzegelcode

A postzegelcode is a hand-written method of franking in the Netherlands. It consists of a code containing nine numbers and letters that customers can purchase online from PostNL and write directly on their piece of mail within five days as proof of payment in place of a postage stamp.
Postzegelcode 是荷兰的一种手写邮资盖章方法。它由一个包含九个数字和字母的代码组成，客户可以从 PostNL 在线购买，并在五天内直接写在邮件上，以代替邮票作为付款证明。

For mail within the Netherlands, the nine letters and numbers are written in a three-by-three grid. For international mail there is a fourth additional row that contains P, N, L.
对于荷兰境内的邮件，九个字母和数字以三乘三的网格形式书写。对于国际邮件，还有第四行，其中包含 P、N、L。

The system was started in 2013. Initially the postzegelcode was more expensive than a stamp because additional handling systems were required. Then for a while the postzegelcode was cheaper. Eventually the rates were set to the same price.
该系统于 2013 年启动。最初，postzegelcode 比邮票更贵，因为需要额外的处理系统。后来有一段时间，postzegelcode 更便宜。最终费率被设定为相同的价格。

In December 2020, 590,000 people sent cards with postzegelcodes.
2020 年 12 月，有 590,000 人使用 postzegelcode 寄出了卡片。

Safety 安全

Since the codes are valid for only five days, the chance that someone would guess a recently purchased code is quite low. Assuming 26 letters and 9 digits (the zero is not used to avoid confusion with the letter O), there are 35 (78.8 trillion) possibilities. Even if a postzegelcode were used for all mail items in the Netherlands, the probability is about 1 in 2 million that any stamp code has been sold in the past five days.
由于代码有效期仅为五天，因此有人猜出最近购买的代码的可能性非常低。假设有 26 个字母和 9 个数字（不使用零以避免与字母 O 混淆），则有 35（78.8 万亿）种可能性。即使荷兰所有邮件都使用 postzegelcode，过去五天内任何邮票代码被出售的概率也约为 200 万分之一。

import random
import string

# 不使用零以避免与字母 O 混淆
CHARACTERS = string.ascii_uppercase + '123456789'

def generate_postzegelcode(international=False):
    # 随机选择 9 个字符
    code = ''.join(random.choice(CHARACTERS) for _ in range(9))

    # 如果是国际邮件，添加额外的一行 "PNL"
    if international:
        code += 'PNL'

    # 按照网格格式展示国内邮件的编码
    grid = [code[i:i+3] for i in range(0, len(code), 3)]

    # 返回邮票编码，按网格排列
    return '-'.join(grid)